Fluid transport systems are well known and used in a number of applications. One specific application of transporting a fluid in a machine is the transportation of ink in a printer. Common examples of inks include aqueous inks and phase change or solid inks. Aqueous inks remain in a liquid form when stored prior to being used in imaging operations. Solid ink or phase change inks typically have a solid form, either as pellets or as ink sticks of colored ink, which are inserted into feed channels in a printer through openings to the channels. After the ink sticks are fed into the printer, they are urged by gravity or a mechanical actuator to a heater assembly of the printer. The heater assembly includes a heater and a melt plate. The heater, which converts electrical energy into heat, is positioned proximate the melt plate to heat the melt plate to a temperature that melts an ink stick coming into contact with the melt plate. The melt plate can be oriented to drip melted ink into a reservoir and the ink stored in the reservoir continues to be heated while awaiting subsequent use.
Fluid couplings in the printer supply the liquid ink held in each reservoir of colored ink to one or more printheads in the inkjet printing apparatus. The liquid ink is pumped from the reservoir to a manifold in the inkjet printing apparatus. As the inkjets in the printheads eject ink onto a receiving medium or imaging member, the action of the diaphragms in the inkjets pulls ink from the manifold. Various embodiments of inkjets include piezoelectric and thermal devices that are selectively activated by a controller with an electrical firing signal.
Phase change ink printers often include one or more heaters that maintain a supply of phase change ink in a liquid state for use during printing operations. Some of the heaters maintain a small supply of ink in the liquid state within the pressure chambers and other fluid conduits within a printhead. Typically, the heaters are electrical heaters that consume electrical energy to maintain the phase change ink in a liquid phase. In order to reduce energy usage, phase change ink printers deactivate various components, including heaters, in the printer during a sleep mode to conserve energy. The ink held in the printheads and inkjets cools and solidifies in some sleep modes.
While sleep modes enable a printer to operate with reduced electrical energy consumption, the solidification of phase change ink within the printer presents difficulties to printing high quality documents when the printer emerges from sleep mode. As phase change ink within an inkjet printing apparatus cools and solidifies, the ink contracts and air enters the pressure chambers and fluid conduits within the printheads. As the solidified ink heats and liquefies during a subsequent warmup process, the air forms bubbles in the liquefied ink that can prevent inkjets in the printheads from operating reliably. Additionally, during the warmup process, both the ink and air bubbles expand due to the heat applied to the printheads. The expanding air bubbles may force some ink through the ejector nozzles, which is referred to as “drooling.” The drooled ink can contaminate other nozzles in the printheads or separate from the printheads and produce errant marks on the image receiving member.
To eliminate air bubbles in the liquefied ink within the printheads and to clear contaminants from the inkjet nozzles and external face of each printhead, the inkjet printing apparatus undergoes a “purge” operation where pressure applied to the printheads urges the liquid ink and the air bubbles through the nozzles of the inkjets. In a purge operation, the inkjets emit a stream of ink that flows down the face of the printhead and is collected in a waste ink receptacle instead of being ejected as individual ink drops. The purge operation removes air bubbles from the inkjets in the printheads and other fluid conduits in the inkjet printing apparatus.
In some printing apparatus designs, a wiping operation occurs after the purge operation. In a wiping operation, a wiper blade engages the face of a printhead and moves across the printhead face, including the inkjet nozzles. The wiper blade cleans residual ink and contaminants on the face of the printhead from the purge operation. The wiping operation maintains the meniscus formed between the liquid ink and nozzle in each of the inkjets in the printhead. The meniscus may be broken if the liquid ink contacts a contaminant or another mass of liquefied ink on the face of the printhead. The wiping operation clears the contaminants to enable each inkjet to maintain the meniscus for reliable operation.
In existing printers, the purged ink and ink from a wiping operation is typically collected in a waste reservoir and is eventually discarded. In printers that enter sleep modes more often to reduce electrical energy consumption, the number of purge cycles and the corresponding amount of discarded ink increases. Thus, improvements to phase change ink printers that reduce or eliminate discarded ink produced during purge cycles are desirable.